Conspicuous deepwater submarine mounds in the northeastern Orphan Basin and on the Orphan Knoll, offshore Newfoundland

Enigmatic Deep-Water Mounds on the Orphan Knoll, Labrador Sea

“…Michael Enachescu (2004) re-examined two commercial Husky Oil deep seismic profiles run in Orphan Basin to the west of Orphan Knoll. These 2000-2003 2D multi-channel seismic lines crossed the western flanks of Orphan Knoll and ran partway onto the flatter top of the feature to the east.…”

“…These 2000-2003 2D multi-channel seismic lines crossed the western flanks of Orphan Knoll and ran partway onto the flatter top of the feature to the east. Enachescu (2004) identified two features that he called "geo-mounds, " which appeared to have possibly grown up through the ca. 150 m of Quaternary hemipelagic sediment cover, and were visible as small "geo-mounds" in the present-day bathymetry.…”

“…This deeper water succession overlies 50 m of shallow water limestones, of Aptian-Cenomanian (mid Cretaceous) age (lower unit 4), unconformably overlying middle Jurassic (Bajocian) terrestrial sandstones and shales. In seismic profiles these Jurassic strata overlie Appalachian crystalline basement (Enachescu, 2004).…”

“…The range of biogenic and abiogenic processes responsible for mound formation is considerable. Some examples of the more common abiotic processes of mound formation, include tectonism and block-faulting (e.g., Laughton et al, 1972;Sibuet, 1992;Moscardelli et al, 2013, reviewed by Cormier andSloan, 2018); magmatic volcanism (e.g., Wiles et al, 2014, reviewed by Casalbore, 2018, and diapirism (e.g., Laughton et al, 1972), often associated with rifting or failed rifts; salt diapirs (e.g., Laughton et al, 1972;Parson et al, 1984), mud volcanoes and similar structures related to fluid escape (e.g., Barrett et al, 1988;Bolton et al, 1988;Enachescu, 2004;Burton-Ferguson et al, 2006, reviewed by Mazzini andEtiope, 2017); cold-seeps and authigenic carbonate precipitation (reviewed by Ceramicola et al, 2018); some types of contourite drifts (reviewed by Esentia et al, 2018) and submerged subaerial erosion features such as karst (Hart, 1977;Parson et al, 1984;Dronov, 1993;Immenhauser and Rameil, 2011;Taviani et al, 2012). Biogenic mounds in the deep sea include, a variety of types of biogenic carbonate mound formation including cold-water coral reefs and mounds (e.g., Hovland et al, 1994;Huvenne et al, 2003;Roberts et al, 2003, reviewed by Lo Iacono et al, 2018, and siliciclasticdominated sponge reefs (e.g., Conway et al, 2005;Howell et al, 2016) and microbial mounds (e.g., Riding and Awramik, 2000).…”

“…Interest in Orphan Knoll and the Orphan Knoll mounds re-emerged in the late 1990s and early 2000s when late Pleistocene and Holocene solitary scleractinian corals collected in the 1978 Geological Survey of Canada exploration of Orphan Knoll (Keen, 1978) were reanalyzed for paleoceanographic investigations (e.g., Smith et al, 1997). The cold-water coral research on the Orphan Knoll, combined with previous studies on carbonate rock samples from the Knoll (Legault, 1982;Parson et al, 1984;van Hinte et al, 1995) raised the possibility that the Orphan Knoll mounds were biogenic carbonate mounds (Enachescu, 2004). Accordingly, Orphan Knoll was eventually protected from deep-water fishing activity by a Northwest Atlantic Fisheries Organization (NAFO) closure (Thompson and Campanis, 2007), despite the fact that the nature of the mounds, and the nature of the coral fauna, were not yet well-understood.…”